The present invention relates to a plasma etching method for performing an etching with using plasma.
A silicon oxide film and a silicon nitride film have excellent characteristics for an insulating film. Therefore, the silicon oxide film and the silicon nitride film are used in many processes in manufacturing of a semiconductor device. In a manufacturing process for a semiconductor device, there are many processes for etching a silicon nitride film formed on a silicon oxide film. For example, there is a manufacturing process for a spacer structure arranged on both sides of a gate electrode in formation of a doping layer in a transistor. In the spacer structure, in general, a silicon nitride film is used. The silicon nitride film is formed on a silicon oxide film formed around the gate electrode. The spacer structure is manufactured by etching the silicon nitride film. The silicon oxide film is used as a stopper film in etching the silicon nitride film.
As a technique for increasing an selected etching ratio of such a silicon nitride film, which is formed on the silicon oxide film, to the silicon oxide film, for example, JP-A-10-303187 discloses a technique for etching a silicon nitride film using a fluorocarbon gas such as a CHF3 gas or a CH2F2 gas as an etching gas.
In the technique disclosed in JP-A-10-303187, the silicon nitride film is etched on the basis of a radical reaction involving a fluorine radical (F*) as main etching species. A fluorocarbon deposited film is deposited on the silicon oxide film. This makes it possible to reduce etching speed and increase the selected etching ratio to the silicon oxide film.